ok i will answer this in two parts, firstly i hated that bumper, it rattled like anything, having said that i am not a fan of big body kits anyway, as i explained in my earlier comment, if it were upto me i would keep it stock looking with small lips at the most...as my previous project cars were, I only care about performance....but i cant have it like that so this how it ends up.
and ur right, this is not a diffuser anything but, this is just style that has been taken from one, may be in some time i will try to find a solution to make both the bumpers look simplish, it was just not the priority at this stage... when i drive and floor it, it puts the biggest smile on my face, and i forget abt cosmetics 